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How to Use a Thermometer

Two Parts:

Fevers are reflective of an increase in your body temperature. Mild fevers are often beneficial because they represent the body trying to defend itself against infections. Many disease-causing (pathogenic) microorganisms thrive in a narrow temperature range, so a mild fever prevents them from reproducing.However, some fevers may be related to connective tissue disease or malignancies. High fevers (103 °F or 39.4 °C or greater for an adult) are potentially dangerous and should be closely monitored with a thermometer. There are many types and models of thermometers meant for different areas of the body. The most appropriate choice is typically determined by the age of the person with the fever — some thermometers are better for small children, for example. Once you've chosen the most appropriate thermometer, using it is relatively straightforward.

Steps

Selecting the Most Appropriate Thermometer

Take rectal temperature readings on newborns.The best or most appropriate type of thermometer and where to measure body temperature depends mostly on age. From birth to about six months of age, using a regular digital thermometer to take a rectal (anal) temperature is recommended because it's considered the most accurate.

Earwax, ear infections, and small, curved ear canals interfere with the accuracy of ear thermometers (also called tympanic thermometers), so they are not the best types to use for newborns.

Some research suggests that temporal artery thermometers are also good options for newborns due to accuracy and reproducibility. The temporal artery can be seen in the temple region of the head.

The American Academy of Pediatrics recommends against using old-style glass thermometers that contain mercury.The glass can break and mercury is poisonous to people, so digital thermometers are safer options.

Choose where to measure temperature on toddlers cautiously.Up to an age of about three years (and maybe as old as five), a rectal reading from a digital thermometer still provides the most accurate reading for core body temperature.You can use a digital ear thermometer at younger ages to get general readings (better than no reading at all), but until about the age of three years or so, readings from the rectum, armpit, and temporal artery are considered more accurate. Because mild-to-moderate fevers in toddlers can be more dangerous than in adults, an accurate temperature reading during the younger years is particularly important.

Ear infections are common and occur with regular frequency in newborns and toddlers, which affect the readings of infrared ear thermometers due to inflammation within the ear. Consequently, ear thermometers typically give overly high readings with ear infections.

Regular digital thermometers are pretty versatile and can record temperatures from the mouth (under the tongue), armpit, or rectum and are appropriate to use on newborns, toddlers, older children, and adults.

Choose any thermometer and measure any area for older children and adults.Beyond three-to-five years of age, kids tend to get fewer ear infections and it's much easier to clean their ears and remove wax build up. Wax in the ear canal prevents ear thermometers from accurately reading the infrared radiation coming off the eardrum.Furthermore, children's ear canals eventually grow and become less curved. Consequently, beyond three-to-five years of age, all types of thermometers used in most areas of the body are pretty comparable in terms of accuracy.

Digital ear thermometers are often considered the quickest, easiest, and least messy way of taking body temperatures.

Using a regular digital thermometer rectally is very accurate, but likely the most unpleasant and messy way of recording body temperature.

Heat sensitive strips that stick onto the forehead are convenient and affordable, but not as precise of accurate compared to digital thermometers.

There are also "forehead" thermometers that are different from plastic strip thermometers. These are more expensive, usually used in the hospital setting, and utilize infrared technology to obtain readings at the temporal region.

Using the Various Thermometers

Use a digital thermometer orally.The mouth (oral cavity) is considered to be a reliable representation for body temperature when the thermometer is placed far back under the tongue.As such, take the digital thermometer out of its holder and turn it on; slide the metal tip into a new disposable plastic cover (if one is available); carefully place it as far back under the tongue as possible; then close your lips gently around the thermometer until it beeps and gives a reading. It may take a few minutes, so breath through your nose while waiting.

If you do not have a disposable cover, clean the end of the probe with soap and warm water (or rubbing alcohol), then rinse it with cool water.

Core temperatures of people average about 98.6 °F or 37 °C (although it varies due to many factors), but oral temperatures taken with a digital thermometer tend to be slightly lower with an average reading of 98.2 °F or 36.8 °C.

Use a digital thermometer rectally.A rectal reading is usually reserved for toddlers and newborns, although it is also very accurate for adults, albeit maybe somewhat uncomfortable. Before inserting a digital thermometer into the anus, make sure to lubricate it with some water-soluble or petroleum-based jelly first.Lubrication is typically placed over the probe cover — it allows for easier insertion and increased comfort. Spread the buttocks (it's easier if the patient is lying on their stomach) and insert the tip of the thermometer no more than 1/2 an inch into the rectum. Never force it if resistance is encountered. Be prepared to wait a minute or more for the thermometer to beep, then slowly remove it.

Be especially thorough while cleaning your hands and thermometer after taking a rectal reading because E. coli bacteria from fecal material can cause serious infections.

For rectal measurements, consider buying a digital thermometer with a fairly flexible tip on the end because it will provide more comfort.

Rectal measurements from digital thermometers can be as much as one degree higher than oral and axillary (armpit) readings.

Use a digital thermometer under the arms.The underarm or axillary area is another place to measure body temperature, although it's not considered as accurate as the mouth, rectum, or ear (tympanic membrane).After putting a probe cover on the tip of the digital thermometer, make sure the armpit is dry before you insert it. Place the probe into the middle of the armpit (pointing upwards toward the head) and then make sure the arm is close to the body so the body heat is trapped. Wait at least a few minutes or until the thermometer beeps with a reading.

Wait at least one hour after heavy exercise or a hot bath before taking body temperature from the axilla or anywhere else.

For better accuracy, take readings from both armpits and then average the two temperatures together.

Axillary measurements with a digital thermometer tend to be lower than other areas, with an average normal temperature being around 97.7 °F (36.5 °C).

Use a tympanic thermometer.A tympanic thermometer is shaped differently from normal digital thermometers because it is specifically designed to fit into the ear canal. Tympanic thermometers sense reflected infrared (heat) emissions from the tympanic membrane (eardrum).Before sticking the thermometer into the ear canal, make sure it's free of wax and dry. Wax buildup and other debris in the ear canal reduces the accuracy of readings. After turning the ear thermometer on and placing a sterile cover on the tip, hold the head still and pull back on the top part of the ear to straighten out the canal and make it easier for insertion. There's no need to touch the eardrum with the tip because the thermometer is designed to take a remote reading. After creating a seal around the thermometer by pressing it against the canal, wait for it to take a reading and beep.

The safest and most effective way to clean ears is by using a few drops of warm olive oil, almond oil, mineral oil or special ear drops to soften the earwax, then rinse it all out (irrigate it) with some squirts of water from a little rubber device made for ear cleaning.Cleaning the ear is easiest if performed after a shower or bath.

Do not use an ear thermometer on an ear that is infected, injured, or recovering from surgery.

An advantage of using an ear thermometer is that, when positioned properly, they are quick and fairly accurate.

Ear thermometers tend to be more expensive than regular digital thermometers, but their cost has come down substantially over the last decade.

Use a plastic strip thermometer.Strip-type thermometers are held against the forehead and are relatively popular for taking children's temperature, but they are quite variable in their accuracy.These thermometers use liquid crystals that react to heat by changing color to show the temperature of the skin, but not inside the body. Strip-type thermometers are usually stuck to the skin of the forehead (horizontally) for at least a minute before they are read. Before applying them, make sure the forehead is not sweating from physical activity or badly sunburned — both situations will affect the reading.

It's difficult to get readings in the 1/10 of degrees because the liquid crystals tend to show a range of temperature when they change color.

For more accuracy, place the strip closer to the temple region of the head (over the pulsating temporal artery near the hairline). The blood in the temporal better reflects the internal core temperature.

Learn how to interpret the readings.Keep in mind that newborns have lower than normal body temperatures compared to adults — typically less than 97 °F, versus a normal of 98.6 °F in adults.Thus, a temperature reading that indicates a mild fever in adults (100 °F or 37.8 °C, for example), could be more significant for a baby or infant. Furthermore, the different types of thermometers have slightly different ranges of normal because they measure body heat from different locations. For example, your child has a fever if they: have a rectal or ear temperature reading of 100.4 °F (38 °C) or higher, an oral reading of 100 °F (37.8 °C) or higher, and/or an armpit reading of 99 °F (37.2 °C) or higher.

In general, contact your doctor if: your baby (3 months or younger) has a rectal temperature of 100.4 °F (38 °C) or higher; your infant (three to six months of age) has a rectal or ear temperature greater than 102 °F (38.9 °C); your child (six to 24 months of age) and has a temperature reading over 102 °F (38.9 °C) on any thermometer that lasts longer than a day.

Most healthy adults can tolerate fevers as high as 103 – 104 °F (39 – 40 °C) for short periods of time without having problems. However, temperatures between 105.8 – 109.4 °F (41 – 43°C), termed hyperpyrexia, are serious and require medical attention. Temperatures above 109.4 °F (43 °C) are almost always fatal (deadly).

Community Q&A

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Question

How long do I need to hold a thermometer under my arm to measure the temperature?

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Community Answer

A beeping noise will start. Once that starts, the thermometer is ready and the temperature will be displayed on the screen.

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Question

What is an in/out thermometer?

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Community Answer

It tells both the indoor and outdoor temperatures.

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Question

My digital thermometer does not beep or register a number, why?

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Community Answer

Most likely, it has either run out of power or is broken. Try recharging/replacing the battery, or replacing the thermometer.

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Question

If I remove the plastic sleeve does it affect the reading for tympanic thermometers?

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Community Answer

Yes, this will affect the reading. Tympanic thermometers are supposed to be used with the plastic sleeve to determine an accurate temperature.

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Question

How long do I keep the thermometer under my tongue?

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Community Answer

It depends on the thermometer. Some thermometers will beep when they have found your temperature. If you are using an older thermometer, wait until a thermometer has stopped going up/down, usually between 5-10 minutes.

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Question

Are there any dangerous effects from frequently taking a newborn's temperature?

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Community Answer

No, taking the temperature any number of times will have no effect as such (assuming the thermometer is clean at any given time). Physical contact with glass has no side-effects.

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Question

How do I change my thermometer c to F?

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Community Answer

It honestly depends on the model or a thermometer you have, so just google the thermometer you have and it should tell you how to change it.

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Unanswered Questions

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Read the directions included with the thermometer carefully. Although most digital thermometers function in generally the same way, you want to make sure you understand how to use your specific instrument perfectly.

Prepare the thermometer to read temperatures by pressing the button to turn it on — but make sure the reading is at zero before you slip the disposable plastic sleeve over the probe's tip.

Digital thermometer sleeves are available anywhere thermometers are sold (grocery stores, pharmacies, etc.). They're inexpensive and usually a one-size-fits-all product.

Babies may not regulate their body temperature very well when they're sick, and they may become cooler rather than warmer and feverish.

Wait about 15 minutes before taking your temperature if you've had a warm or cold beverage.

Warnings

An ear temperature of 100.4 °F (38 °C) or greater is consider a fever, but if your child is older than one year and is drinking lots of fluids, playful and sleeping normally, there's usually no reason or need to treat it. However,

Temperatures of around 102 °F (38.9 °C) or greater combined with symptoms such as unusual irritability, discomfort, lethargy, and moderate-to-severe coughing and/or diarrhea, warrant a trip to the doctor.

Symptoms of high fevers (103 – 106 °F or 39.4 – 41.1 °C) often include hallucinations, confusion, severe irritability and convulsions — they are considered medical emergencies and you should seek emergency care immediately.